Leftwich fractured two ribs in Sunday night's 13-10 loss to the Baltimore Ravens.
"Byron Leftwich is out with a rib fracture that he sustained late in the football game," Tomlin said.
Leftwich also hurt his shoulder, but sources said it was not believed to be as damaging as the rib injuries.
Batch, 37, made his last start Dec. 24, 2011, completing 15 of 22 passes for 208 yards and a touchdown in a 27-0 victory over the St. Louis Rams.
Tomlin also offered an update on quarterback Ben Roethlisberger, calling him doubtful for this week.
Roethlisberger missed Sunday's game against the Ravens (8-2) because of a rare dislocated rib injury. Steelers doctors believe Roethlisberger will miss three weeks, though the team has not abandoned hope that he may miss only two games and be able to return for the rematch Dec. 2.
Information from ESPN senior NFL analyst Chris Mortensen and ESPN NFL Insider Adam Schefter was used in this report.